Writing Positron Decay and Electron Capture Equations

Alpha Decay & Beta Decay     Neutron Emission and Capture
Gamma Decay     Proton Emission and Capture
Spontaneous Fission     Radioactivity Menu

A Brief Tutorial About Writing Nuclear Symbols


Positron Decay

Positron decay is like a mirror image of beta decay. These points present a simplified view of what positron decay actually is:

1) Something inside the nucleus of an atom breaks down, which causes a proton to become a neutron.
2) It emits a positron and a neutrino which go zooming off into space.
3) The atomic number goes DOWN by one and mass number remains unchanged.

Example #1: A positron decay equation:

1223 Mg  --->  1123 Na  +  +1  0 e  +  νe

Some points to be made about the equation:

1) The nuclide that decays is the one on the left-hand side of the equation.
2) The order of the nuclides on the right-hand side can be in any order.
3) The way it is written above is the usual way.
4) The mass number and atomic number of the neutrino are zero.
5) The neutrino symbol is the Greek letter "nu."

Example #2: Here is another example of a positron decay equation:

2550 Mn  --->  2450 Cr  +  +1  0 e  +  νe

Notice that all the atomic numbers on both sides ADD UP TO THE SAME VALUE and the same for the mass numbers.

By the way, an older style for the neutrino symbol adds on two zeros where the atomic number and the mass number are placed, as well as dropping the subscripted e. I couldn't make the formatting work, so I have to describe it in words. You might wind up with an older teacher who insists on the older style of writing the neutrino. Or, you might be using an older set of materials.


Example #3: Write out the full positron decay equation for these five.

3575 Br     1530 P     1427 Si     2245 Ti     58 B

Solution:

3575 Br  --->  3475 Se  +  +1  0 e  +  νe
 
1530 P  --->  1430 Si  +  +1  0 e  +  νe
 
1427 Si  --->  1327 Al  +  +1  0 e  +  νe
 
2245 Ti  --->  2145 Sc  +  +1  0 e  +  νe
 
58 B  --->  48 Be  +  +1  0 e  +  νe

Example #4: Here are five more to work on. Sometimes, the teacher wants the neutrino left off the answer. That's what I did with the answers.

  713 N     1937 K     2754 Co     3061 Zn     3168 Ga

Solution:

  713 N  --->    613 C  +  +1  0 e
 
1937 K  --->  1837 Ar  +  +1  0 e
 
2754 Co  --->  2654 Fe  +  +1  0 e
 
3061 Zn  --->  2961 Cu  +  +1  0 e
 
3168 Ga  --->  3068 Zn  +  +1  0 e

Example #5: And here are five more. I'll only show the daughter nuclide:

  815 O       918 F     2039 Ca     3883 Sr       66155 Dy

Solution:

  815 O  --->    715 N
 
  918 F  --->    818 O
 
2039 Ca  --->  1939 K
 
3883 Sr  --->  3783 Rb
 
  66155 Dy  --->    65155 Tb

Bonus Example: Five more, but no answers.

1121 Na     1325 Al     1630 S     2142 Sc     2960 Cu

Electron Capture

Electron capture is not like the other three decays I have covered: alpha, beta, and position. All other decays shoot something out of the nucleus. In electron capture, something ENTERS the nucleus. These points present a simplified view of what electron capture is:

1) An electron from the closest energy level falls into the nucleus, which causes a proton to become a neutron.
2) A neutrino is emitted from the nucleus.
3) Another electron falls into the empty energy level and so on causing a cascade of electrons falling. One free electron, moving about in space, falls into the outermost empty level. (Incidently, this cascade of electrons falling creates a characteristic cascade of lines, mostly (I think) in the X-ray portion of the spectrum. This is the fingerprint of electron capture.)
4) The atomic number goes DOWN by one and mass number remains unchanged.

Example #1: Here is an example of a electron capture equation:

3681 Kr  +  –1  0 e  --->  3581 Br  +  νe

Some points to be made about the equation:

1) The nuclide that decays is the one on the left-hand side of the equation.
2) The electron must also be written on the left-hand side.
3) A neutrino is involved. It is ejected from the nucleus where the electron reacts, so it is written on the right-hand side.

Example #2: Here's another electron capture equation:

  96239 Cm  +  –1  0 e  --->    95239 Am  +  νe

Notice that all the atomic numbers on both sides ADD UP TO THE SAME VALUE and the same for the mass numbers.

Example #3: Write out the full electron capture equation for the following five nuclides.

1838 Ar     3880 Sr       53125 I       69168 Tm       99247 Es

Solution:

1838 Ar  +  –1  0 e  --->  1738 Cl  +  νe
 
3880 Sr  +  –1  0 e  --->  3780 Rb  +  νe
 
  53125 I  +  –1  0 e  --->    52125 Te  +  νe
 
  69168 TM  +  –1  0 e  --->    68168 Er  +  νe
 
  99247 Es  +  –1  0 e  --->    98247 Cf  +  νe

Example #4: Here are five more to work on. I left off the neutrino.

2757 Co     3373 As       56128 Ba       62145 Sm       84200 Po

Solution:

2757 Ar  +  –1  0 e  --->  2657 Fe
 
3373 As  +  –1  0 e  --->  3273 Ge
 
  56128 Ba  +  –1  0 e  --->    55128 Cs
 
  62145 Sm  +  –1  0 e  --->    61145 Pm
 
  84200 Po  +  –1  0 e  --->    83200 Bi

Example #5: And a final five, with just the daughter nuclide:

3167 Ga     4497 Ru       85200 At       94235 Pu     101257 Md

Solution:

3167 Ga  --->  3067 Zn
 
4497 Ru  --->  4397 Tc
 
  85200 At  --->    84200 Po
 
  94235 Pu  --->    93235 Np
 
101257 Md  --->  100257 Fm

Bonus Example: Five more, but no answers.

2350 V     2451 Cr     2856 Ni     4191 Nb       97244 Bk

Nov. 21, 2020 − I continue to learn new things! There is something called a double electron capture. About 34 nuclei are predicted to undergo double electron capture, but only three have been observed. The Wikipedia page has more information on this rare decay.

Before heading over there, you might try writing the double electron capture equation for   56130 Ba . The answer is on the Wiki page.


Alpha Decay & Beta Decay     Neutron Emission and Capture
Gamma Decay     Proton Emission and Capture
Spontaneous Fission     Radioactivity Menu